• 한국수소및신에너지학회논문집
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• 제32권5호
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• pp.340-346
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• 2021

The initial electrochemical performance of ceramic fuel cell with thin-film electrolyte fabricated by plasma-enhanced atomic layer deposition method was evaluated in terms of peak power density ratio, open circuit voltage ratio, and activation/ohmic resistance ratios at 500℃. Hydrogen and air were used as anode fuel and cathode fuel, respectively. The peak power density ratio reduced as ~52% for 30 min, which continually decreased as time increased but degradation rate gradually decreased. The open circuit voltage ratio decreased with respect time; however, its behavior was evidently different from the reduction behavior of the peak power density. The activation resistance ratio increased as ~127% for 30 min, which was almost similar with the reduction behavior of the peak power density ratio.

• 한국전기전자재료학회논문지
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• 제30권3호
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• pp.175-179
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• 2017

In this study, we investigate the $SiO_2$ current blocking layer (CBL) to improve light output power efficiency in nonpolar a-plane (11-20) GaN LEDs on a r-plane sapphire substrate. The $SiO_2$ CBL was produced under the p-pad layer using plasma enhanced chemical vapor deposition (PECVD). The results show that nonpolar GaN LED light output power with the $SiO_2$ CBL is considerably enhanced compared without the $SiO_2$ CBL. This can be attributed to reduced light absorption at the p-pad due to current blocking to the active layer by the $SiO_2$ CBL.

• Journal of Magnetics
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• 제14권1호
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• pp.31-35
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• 2009

Herein, the Magneto-Optical Kerr Effect (MOKE) signal enhancement in nanostructures in investigated. It is well known that the MOKE signals of ferromagnetic thin films are enhanced with an additional dielectric layer due to multiple reflections. The MOKE signal is modulated with the additional dielectric layer thickness and is at a maximum when reflectivity is at a minimum. This is not always true in the nanostructures due to the contribution from the non-magnetic substrate portion, especially when substrate reflectivity is minimized and the dependence of the additional dielectric layer thickness for the nanostructure is changed in the case of the continuous thin film. We showed that the MOKE signal for nanostructures could be enhanced with a properly designed, dielectric layer in addition to the anti-reflection coated substrates.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.636-636
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• 2013

Since first discovery of strong Raman spectrum of molecules adsorbed on rough noble metal, surface enhanced Raman scattering (SERS) has been widely used for detection of molecules with low concentration. Surface plasmons at noble metal can enhance Raman spectrum and using Au nanostructures as substrates of SERS has advantages due to it has chemical stability and biocompatibility. However, the photoluminescence (PL) background from Au remains a problem because of obtaining molecular vibration information. Recently, graphene, two-dimensional atomic layer of carbon atoms, is also well known as PL quenchers for electronic and vibrational excitation. In this study, we observed SERS of single layer graphene on or under monolayer of Au nanoparticles (NPs). Single layer graphene is grown by chemical vapor deposition and transferred onto or under the monolayer of Au NPs by using PMMA transfer method. Monolayer of Au NPs prepared using Langmuir-Blodgett method on or under graphene surface provides closed and well-packed monolayer of Au NPs. Scanning electron microscopy (SEM) and Raman spectroscopy (WItec, 532 nm) were performed in order to confirm effects of Au NPs on enhanced Raman spectrum. Highly enhanced Raman signal of graphene by Au NPs were observed due to many hot-spots at gap of closed well-packed Au NPs. The results showed that single layer graphene provides larger SERS effects compared to multilayer graphene and the enhancement of the G band was larger than that of 2D band. Moreover, we confirm the appearance of D band in this study that is not clear in normal Raman spectrum. In our study, D band appearance is ascribed to the SERS effect resulted from defects induced graphene on Au NPs. Monolayer film of Au NPs under the graphene provided more highly enhanced graphene Raman signal compared to that on the graphene. The Au NPs-graphene SERS substrate can be possibly applied to biochemical sensing applications requiring highly sensitive and selective assays.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권12호
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• pp.6017-6037
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• 2017

In a multi-resolution image encoding system, the image is encoded into a single file as a layer of bit streams, and then it is transmitted layer by layer progressively to reduce the transmission time across a low bandwidth connection. This encoding scheme is also suitable for multiple decoders, each with different capabilities ranging from a handheld device to a PC. In our previous work, we proposed an edge adaptive hierarchical interpolation algorithm for multi-resolution image coding system. In this paper, we enhanced its compression efficiency by adding three major components. First, its prediction accuracy is improved using context adaptive error modeling as a feedback. Second, the conditional probability of prediction errors is sharpened by removing the sign redundancy among local prediction errors by applying sign flipping. Third, the conditional probability is sharpened further by reducing the number of distinct error symbols using error remapping function. Experimental results on benchmark data sets reveal that the enhanced algorithm achieves a better compression bit rate than our previous algorithm and other algorithms. It is shown that compression bit rate is much better for images that are rich in directional edges and textures. The enhanced algorithm also shows better rate-distortion performance and visual quality at the intermediate stages of progressive image transmission.

• 방송공학회논문지
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• 제2권2호
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• pp.206-215
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• 1997

본 논문에서는 H.263비디오 압축 표준을 기반으로 한 비디오 부호기들로서 두 개의 계층을 갖는 비트율 계위 비디오 부호기를 제안한다. 제안하는 부호기의 기본계층에서는 H.263표준에서 제안하고 있는 기본 부호기 알고리즘을 수용하여 비디오 데이터의 고 압축 부호화 효율을 얻는다. 상위계층에서는 부호화의 고급 기법이라 하루 수 있는 인간 시각 시스템 정보를 근거로 양자화를 설계하고 적용한다. 상위계층에서는 기본계층의 이산 여현 변환 계수에 보다 세밀한 양자화를 가하여 부호화하게 되며, 이때 필요한 비트스트림의 구조를 설계한다. 복호화기에서는 두 계층에서 수신한 데이터를 역양자화 및 역변환을 수행한 후 더하여 원 영상을 복원하게 된다. 실험 결과를 통하여 비트율 약30kbps 정도에서 계층을 적용하지 않은 부호기와 비교하여 거의 비슷한 화질을 얻을 수 있었으며, 상위계층의 비트스트림을 전송하기 위한 부가 정보를 약 프레임당 0.5kbits이하를 유지하도록 하였다.

• 한국전기전자재료학회논문지
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• 제29권8호
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• pp.505-509
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• 2016

We have investigated the characteristics of amorphous silicon (a-Si) thin-film solar cell by inserting barrier layer. The conversion efficiency of a-Si thin-film solar cells on graphite substrate shows nearly zero because of the surface roughness of the graphite substrate. To enhance the performance of solar cells, the surface morphology of the back side were modified by changing the barrier layer on graphite. The surface roughness of graphite substrate with the barrier layer grown by plasma enhanced chemical vapor deposition (PECVD) reduced from ~2 um to ~75 nm. In this study, the combination of the barrier layer on graphite substrate is important to increase solar cell efficiency. We achieved ~ 7.8% cell efficiency for an a-Si thin-film solar cell on graphite substrate with SiNx/SiOx stack barrier layer.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.256-256
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• 2011

We have deposited Al2O3 thin films on Si substrates at room temperature by UV-enhanced atomic layer deposition using trimethylaluminum (TMA) and H2O as precursors with UV light. The atomic layer deposition relies on alternate pulsing of the precursor gases onto the substrate surface and subsequent chemisorption of the precursors. In many cases, the surface reactions of the atomic layer deposition are not completed at low temperature. In this experiment, the surface reactions were found to be self-limiting and complementary enough to yield uniform Al2O3 thin films by using UV irradiation at room temperature. The UV light was very effective to obtain the high quality Al2O3 thin films with defectless.

• Korean Journal of Chemical Engineering
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• 제35권12호
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• pp.2474-2479
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• 2018

Plasma-enhanced atomic layer deposition (PEALD) is well-known for fabricating conformal and uniform films with a well-controlled thickness at the atomic level over any type of supporting substrate. We prepared nickel oxide (NiO) thin films via PEALD using bis(ethylcyclopentadienyl)-nickel ($Ni(EtCp)_2$) and $O_2$ plasma. To optimize the PEALD process, the effects of parameters such as the precursor pulsing time, purging time, $O_2$ plasma exposure time, and power were examined. The optimal PEALD process has a wide deposition-temperature range of $100-325^{\circ}C$ and a growth rate of $0.037{\pm}0.002nm$ per cycle. The NiO films deposited on a silicon substrate with a high aspect ratio exhibited excellent conformality and high linearity with respect to the number of PEALD cycles, without nucleation delay.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.283-284
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• 2008

A cross-layer optimization is becoming a popular design methodology for the IP based next generation wireless network. We begin by investigating a cross-layer optimization scheme to enhance the system performance in wireless networks. By applying cross-layer optimization methodology to WiBro distributed network, the WiBro systems are expected to gain significant performance improvement and resource utilization enhanced. For further study we highlight some open challenges and new opportunities for cross-layer design.